Corrosion-inhibiting titanium dioxide pigments



United States Patent ()fiice 3,345,187 Patented Oct. 3, 1967 3,345,187 CORROSION-INHIBITING TITANIUM DIOXIDE I PIGMENTS KennethBinnis, Stockton-on-Tees, England, assignor to British Titan Products Company Limited, Durham, England, a corporation of the United Kingdom No Drawing. Filed June 9, 1965, Ser. No. 462,744 Claims priority, application Great Britain, July 31, 1964, 30,361/64 9 Claims. (Cl. 106-14) ABSTRACT OF THE DHSCLOSURE Corrosion-inhibiting surface coating compositions, and in particular, primers, normally require the use of pigments which are highly colored. By coating titanium dioxide pigment particles with triisopropanolamine or the benzoates thereof or with the titanates or phosphates of the trialkanolamines such as triethanolamine or triisopropanolamine, an improved pigmentary product is obtained which may be used in primer coatings without the problems associated with the use of highly colored pigments.

- The present invention relates to improved pigments for use in corrosion-inhibiting surface coating compositions and to the compositions containing them.

Corrosion-inhibiting surface coating compositions, particularly priming compositions for application to the surface of ferrous metals, suffer from a number of disadvantages. For example, the pigments having corrosioninhibiting properties which are used in such compositions are usually highly coloured and where the structure to which the corrosion-inhibiting composition is applied is to be finished by the application of a decorative coating, for example, an oleoresinous gloss paint, it is frequently necessary to cover the corrosion-inhibiting coating composition with an undercoat of the appropriate colour before the final decorative coat can be satisfactorily applied. This is, of course, particularly necessary when the final coating is light in colour.

In addition, previously used corrosion-inhibiting pigments have a lower opacity than TiO pigments and the present invention provides pigments of increased opacity combined with corrosion-inhibiting properties.

The pigments of the present invention are provided with a coating of corrosion-inhibiting material on the sur face of the pigmentary particles, thus the corrosioninhibiting material is placed where it achieves the greatest effect and is used most efiiciently.

It is an object of this invention to provide improved pigments for use in surface coating compositions, particularly those having corrosion-inhibiting properties, and compositions containing the pigments.

Accordingly, the present invention comprises pigmentary titanium dioxide particles coated with a compound selected from triisopropanolamine and the benzoates thereof and the titanates and phosphates of an alkanolamine of the general formula /ROH NROH ROH where R represents a divalent aliphatic radical which may be the same or different containing 2 or 3 carbon atoms.

The invention also includes a process comprising coating pigmentary titanium dioxide particles with compounds selected from the above group and surface coating compositions containing the coated pigmentary titanium dioxide particles of the present invention.

The titanium dioxide particles of the present invention are preferably of pigmentary size, for example having a mean weight particle size in the range 0.15 micron to 0.35 micron and particularly in the range 0.2 micron to 0.3 micron. Where they are predominantly of the rutile modification they should preferably contain at least and preferably at least of this form.

The particles may or may not be coated with materials other than those of the present invention but it is preferred that there should be present on the particles a coating of at least one other material, for example a metal oxide (which term includes silica).

Examples of metal oxides which may be present are oxides of aluminium, titanium, cerium, zirconium and/or silicon. Such oxides are conveniently applied, either singly or in combination, before the coatings of the present invention, in amounts in the range from 0.1% to 5%, particularly from 0.5% to 3% (by Weight on TiO The pigment particles may also be coated with a phosphate, for example of aluminium, titanium, zirconium or cerium. An amount of phosphate (as P 0 in the range 0.1% to 3%, by Weight on TiO has been found very suitable.

The presence of a coating of material such as a metal oxide, particularly of aluminium oxide, is believed to assist in forming a surface upon the particles which is particularly receptive to the coatings of the present invention.

The coating compounds of the present invention may be liquids or solids, for example triethanolamine titanate and phosphate are normally viscous liquids. Tri-isopropanolamine is normally a solid of low melting point, and the titanate of this compound is generally a liquid and the phosphate a solid. The benzoate is a water-soluble compound which may be conveniently made by mixing the base and benzoic acid in water to give an aqueous solution of the compound.

The compound may, of course, exist in different physical forms depending upon the conditions, for example, the temperature. In the case of the titanates, at least, the

physical form (i.e. liquid or solid) may also depend upon I the degree of polymerisation and the most convenient method of applying the compounds to the titanium dioxide particles will depend upon the properties of the available product.

Where the compound can be applied at temperatures in the range of about 80 C. to 250 C. it is very convenient to apply the material during fluid energy milling of the titanium dioxide by introducing the material into the mill either with the pigment or separately. Alternatively, the compound may be applied in solution in an organic solvent or in Water or, where appropriate, they may be melted and applied in the liquid state. Under such circumstances the solution or melt may be poured or sprayed onto the particles, preferably before milling the particles to break down aggregates which may be formed during the addition. Triisopropanolamine benzoate is preferably applied to the pigment in aqueous solution.

Suflicient of the compound is preferably applied to the pigment particles by any suitable method to allow the particles to retain, an amount of the added compound in the range of about 0.5 to 5% particularly an amount in the range 1% to 3%, by weight on TiO The surface coating compositions containing the coated titanium dioxide particles of the present invention are generally priming compositions containing an organic film-forming material which may, for example, be an alkyd resin or modified alkyd resin such as an oilor epoxy-modified resin or an oil medium such as linseed They may be air drying or stoving compositions.

If desired, water-soluble or water-dispersible resins may be used as the film-forming material, for example media containing alkyd-amino, melamine-acrylic or water-soluble acrylic or phenolic based resins.

applied to burnish mild steel panels 6" x 4 to give a dry film thickness of about 20 microns.

The panels, after standing for 7 days at 20 C. in a relative humidity of 65, were scratched with a cross The coated titanium dioxide particles are normally through the paint film and were then exposed (in quinpresent in the coating composition in a pigment volume tuplicate) in a heavily polluted industrial atmosphere for concentration in the range of about to 50%, parti a period of 12 months. Under these conditions the comularly one in the range 25% to 35%. positions containing the pigment of the present invention The pigments of the present invention retain the inhibitwere found to be generally as effective as similar coating ing properties of the tri-isopropanolamine or alkano 1O compositions containing red lead and better than composiamine compound with the high opacity and high degree O tions containing zinc chromate and calcium plumbate whiteness of the TiO which enables them to be more hi h a w ll kn n lou d corrosion-inhibiting pigreadily covered by a decorative coating. Because of the t latter Properties it y he Possible, When using the Similar coating compositions containing rutile titanium POSiti HS f t e p ent i i n, to i p With an 15 dioxide particles coated with equal quantities of alumina, undercoat. titania and silica but without the organic coatings of the Furthermore, the amount of tri'isopl'opallolamine of present invention were also tested under the same conalkanolamine compound of the present invention required diti it) give acceptable COI'IOSlOIl-lllhlblilOl'l, iS much reduced The results obtained in the exposure tests are givgn in since in the present invention it is present only in the form h bl at th d f thi ifi ti of a layer on the surface of the titanium dioxide particles C t d pangls using th i t of th present i where it is most effective for its purpose and where it is ti a d r d i a i il manner t th t d ib d then used most efhcientlyabove were also subjected to the following tests.

The following examples show embodiments of the present invention. Test 1 EXAMPLE 1 This was a salt spray test as set out in Defence Specification DEF 1053, No. 24 using an intermittent salt spray A solution of triethanolamine titanate in alcohol which was applied for a total of 336 hours in a 3 week (85%) was allowed to drip onto a belt feed carrying period rutile titanium dioxide particles which had already been Test H coated with alumina (1.5%), titania (1.12%) and silica (0.5%) to a hopper from which the material was sup- Thls was h t0 I but h Salt 2 l, which plied to a fluid energy mill by steam injection. Sufiicient W h P slmuiate T3111 Water 111 a heavily Polluted triethanolamine titanate was added to the particles in this lndustrlal area, contamed the following ingredientsmanner to allow the retention on the pigment, after fluid energy milling of about 3.2% of triethanolamine titanate Ammomum Sulphate (by weight on i0 Calcium chloride (anhyd) 12.00

The fluid energy milling was carried out using steam at Sodium sulphite 16-30 100 Psig, Sodium sulphate 12.40

A L 2 40 Potassium nitrate 0.065

The process described in Example 1 was repeated gg mtI-lte 0'074 ater to 20 lltres. applying the following compounds in the form noted and in sufficient quantity to allow the retention, after milling, This P Y had P Vahle of about of the concentration shown. Spraying with this solution provides a much more rigorous test of anticorrosion properties than does that given Amount under Test 1. t ede er Similar tests were also carried out on similar coating Compound Form fg' gg gggfi compositions which contained:

s fifif (a) Zinc chromate pigment (b) Calcium plumbate pigment Triethanolamine phosphate. As adliquid at C 11:2 and 2.3. (0) Red lead pigment ifiiifigitfiififiiihifiinaa 6%si ii1'ibi ih'is'6- 1: The results obtained with Tests 1 and n and in the Tfiihopropanolamine Agi z s hi t iiin con- 0.64. exposure t Wei-F graded A B C agains} the resunis benzoate. mining w of the panels which were coated with the palnt composition containing rutile Ti0 pigment coated with 1.5%

The coated titanium dioxide pigments thus produced alumina, 1.12% titania and 0.5% silica but without any were mixed at 32% pigment volume concentration with organic coating. a medium oil length linseed oil-modified alkyd resin and The categories A, B and C varied in each test and they the coating compositions thus produced were separately 60 are noted at the foot of each table.

TEST I Amount of Order of Pigment Organic Coating Organic Category Performance Coating, Percent TiO Trlethanolamine tltanate.-. 3.3 A Calcium plum- A b A Trlethanolamine titanate 1.2 A Tri-isopropanolamine 0.6 A Tri-isopropanolamine 3 A Triethanolamina phosphate. 1.2 is. 0

Nora-Category mated as 20-50% of TEST II Amount of Order of Pigment Organic Coating Organic Category Performance Coating,

Percent T10; 'Iriethanolamine titanate---. 3.2 A Calcium plum- A bate.

Triethanolamine phosphate 2 3 i ffiisbliibfifirifihEIIIIII "5' A Tri-isopropanoiamine 0.65 B 'Iriethanolamine titanate 1.2 B

No'rE.Category A corrosion estimated as to 70% of standard; category B corrosion estimated as 70 to 90% of standard; Category C corrosion estimated as 90 to 100% of standard.

(This test, as previously noted, is very rigorous.) in claim 1 wherein the coating is present on the particles The results of the exposure tests given in column 4 in an amount in the range 0.5% to 5% (by weight on of this specification are shown in the table below. TiO

The results of similar tests with paints containing red 6. Coated pigmentary titanium dioxide particles in aclead, zinc chromate and calcium plumbate pigments precordance with claim lwherein the particles additionally pared as for Test II are also given. have a coating of an oxide selected from the group con- ATMOSPHERE IN HEAVILY POLLUTED AREA.

Triethanolamine phospha Tri-isopropanolamine .do -..do

.do O

A A A A A B B Nora-Category A corrosion estimated as 0% to of standard; category B corrosion estimated as 25% to 60% of standard; category C corrosion estimated as 60% to 100% 01 standard.

The pigments of the present invention, when incorposisting of alumina, titania, ceria, zirconia and silica interrated into the surface coating compositions had in al mediate said titanium dioxide particle and said trialkanolcases markedly superior opacity when compared with the amine titanate coating. other pigments tested. 7. A paint composition consisting of an organic film- What is claimed is: forming medium and pigmentary titanium dioxide par- 1. Pigmentary titanium dioxide particles coated with ticles as claimed in claim 1.

a compound selected from the group consisting of the 8. A paint composition as claimed in claim 7 wherein titanates of alkanolamines of the general formula the organic film-forming medium is selected from the ROH group consisting of linseed oil, a modified linseed oil, an NZROH alkyd resin, a modified alkyd resin, an alkyd amino-, a melamine acrylic-, a water-soluble acrylicand a phenolic- ROH based-resin. wherein each of the Rs are separately selected from the 9- A paint composition as claimed in claim 7 wherein group consisting of divalent aliphatic radicals containing the pigment volume concentration is in the range 15% two carbon atoms and divalent aliphatic radicals containto 50%. ing three carbon atoms. References Cited 2. Coated pigmentary titanium dioxide particles in accordance with claim 1 wherein said coating consists es- UNITED STATES PATENTS sentially of triethanolamine titanate. 1,936,533 11/1933 Albrecht 10614 3. Coated pigmentary titanium dioxide particles in ac- 2,308,282 1/ 1933 Howland 106-14 cordance with claim 1 wherein said coating consists es- 2,671,031 3/1954 Whatley 106-300 sentially of triisopropanolamine titanate. 2,819,174 1/ 1958 Vortanian 106308 4. Pigmentary titanium dioxide particles as claimed in 3,015,573 2/ 1962- Meyer 106308 claim 1 wherein the particles have a mean weight crystal 3,172,772 3/ 1965 Rowe 106-308 size in the range 0.15 to 0.35 I

5. Pigmentary titanium dioxide particles as claimed JULIUS FROME, Primary Examiner. 

1. PIGMENTARY TITANIUM DIOXIDE PARTICLES COATED WITH A COMPOUND SSELECTED FROM THE GROUP CONSISTING OF THE TITANATES OF ALKANOLAMINES OF THE GENERAL FORMULA 